1. Field of the Invention
The present invention relates to welding machines and, more particularly, to welding machines used in automated production lines having temperature sensors coupled to heat generating elements of the welding machine and a controller for determining abnormal temperature conditions of the heat generating elements.
2. Description of the Related Art
Generally, resistance welding machines utilize a large current that passes through a welding gun, a welding cable, a welding transformer and a switching element for controlling a welding current. As a result, these heat generating elements generate heat and typically a cooling device is utilized in the resistance welding machine in order to cool such heat generating elements using water or another cooling medium.
However, if the cooling device malfunctions, the heat generating elements may rise in temperature and may be damaged or destroyed by the excessive heat. In order to protect the heat generating elements from thermal damage, a protective system against excessive heating is typically provided. For example, a bimetal temperature sensitive switch is disposed on each of the heat generating elements and is actuated when the temperature of the associated heat generating element rises to a specified temperature, which temperature is usually a temperature at which parts within the welding machine may be damaged. Thus, if the temperature of any of the heat generating elements, such as the welding transformer, rises to a specified temperature and the bimetal temperature-sensitive switch is actuated during the welding operation, a controller sends a signal to the switching element in order to turn off the welding current.
The temperature of the heat generating elements may excessively increase, thereby actuating the bimetal temperature-sensitive switch, in the following representative situations:
1) the current exceeds a predetermined rated current for the particular heat generating element,
2) the cooling device malfunctions, e.g. due to improper operation or the cooling medium freezes,
3) calcium, magnesium, sand, rust, dust or another (insulating) material is deposited within the cooling device, thereby reducing the ability of the cooling device to conduct heat from the heat generating elements or
4) microorganisms propagate in the cooling water and deposit within the cooling device, thereby clogging the cooling device with such deposits.
Resistance welding machines are typically installed in production lines for vehicle bodies or other similar products. If the bimetal temperature-sensitive switch is actuated during operation because an excessive temperature situation is detected, the welding current is cut off. As a result, the welding operation cannot be continued and the production line must be stopped. In this case, the production line cannot be operated again until the cause of the excess temperature rise is determined and eliminated. Therefore, productivity of the production line may be severely affected.
It is, accordingly, an object of the present teaching to teach improved welding machines.
In one aspect of the present teachings, the welding machine has a device that provides a warning if a heat generating element is approaching an excessive temperature. In this case, an operator is informed of the potentially excessive temperature rise before the temperature of the heat generating element rises pass an upper limit temperature at or above which the welding current is cut off. Thus, remedial action can be taken while the welding machine and the production line is still operating and the problem can be corrected without stopping the production line. Thus, the present welding machines significantly improve productivity over known welding machines.
According to another aspect of the present teachings, the welding machine has an indicator that indicates temperatures of heat generating elements that generate heat due to passage of the welding current. If the temperature indicator indicates a warning signal, the operator can track down and eliminate the cause of a temperature rise of any of the heat generating elements before the temperature of the heat generating element reaches its upper limit temperature.
In another aspect of the present teachings, welding machines may include a memory that is adapted to store data concerning the history of the temperatures of the heat generating elements. A display, a printer or other displaying means may be provided to display the temperature history of one or more heat generating elements. In this case, the operator can study the time-varying temperature conditions of a particular heat generating element in order to assist in determining the cause of a potentially excessive temperature situation.
According to another aspect of the present teachings, the welding machine has a warning device that generates a warning when the temperature of any of the heat generating elements has risen to a potentially excessive temperature, which warning temperature is preferably lower than an upper limit temperature at which the welding current will be shut off. Because the warning device notifies the operator that the temperature of one or more of the heat generating elements has reached the warning temperature, the operator is given early notice of a potential problem. Therefore, the operator can promptly eliminate the cause of the temperature rise of the heat generating element before an excessive temperature situation has occurred. In this case, the warning device may be constructed to operate in a manner that will permit the operator to identify the particular heat generating element that has risen to the warning temperature.
In another aspect of the present teachings, the welding machine has a warning device that provides a warning when the temperature of one or more of the heat generating elements rises by at least a specified amount within a predetermined period of time. Because the operator is notified by the warning device that the temperature of one or more of the heat generating elements has rapidly risen, the operator is notified at an early time of the possibility that the temperature of one or more of the heat generating elements may reach its upper limit temperature in the near future. Again, in this case, the operator can take remedial action at an early time, thereby avoiding a work stoppage.
Additional objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.